In a conventional polymer electrolyte fuel cell (hereinafter, “PEFC”), electric energy produced by an electrochemical reaction in a membrane electrode assembly (hereinafter, “MEA”) that includes a plane electrolyte membrane and electrodes (a cathode and an anode) arranged on both sides of the electrolyte membrane, respectively is extracted to outside via separators provided on both sides of the MEA, respectively. Attention has now been paid to the PEFC as a power source of a battery car or a portable power source because of its operability in a low temperature region, high energy exchange efficiency, short startup time, and small size and light weight as a system.
Meanwhile, a unit cell of the PEFC includes constituent elements such as an electrolyte membrane, a cathode and an anode each including at least a catalyst layer, and separators, and has a theoretical electromotive force of 1.23 V. However, such a theoretical electromotive force is insufficiently low to use as a power source of a battery car or the like. Due to this, a stack PEFC (hereinafter, also simply “fuel cell”) configured to arrange endplates or the like on both ends of a multilayer member, in which unit cells are stacked in series, respectively is normally used. Besides, to further improve power generation performance of the fuel cell, it is preferable to downsize each unit cell and to increase a power generation reaction area (output density) per unit area.
To increase the output density per unit area and to improve the power generation performance of a conventional plane fuel cell (hereinafter, also “plane FC”), it is necessary to make the constituent elements thinner. However, if a thickness of the constituent elements is set to be equal to or smaller than a predetermined thickness, functions, strengths, and the like of the respective constituent elements may possibly decrease. For these reasons, it is structurally difficult to increase the output density per unit area in the fuel cell in the plane form.
From these viewpoints, study about a tubular type PEFC (hereinafter, also “tubular PEFC”) has been recently underway. A unit cell of the tubular PEFC (hereinafter, also “tubular cell”) includes a hollow-shaped MEA (hereinafter, simply “hollow MEA”) including a hollow electrolyte layer and hollow electrodes arranged inside and outside of the electrolyte layer, respectively. An electrochemical reaction is provoked by supplying reaction gases (hydrogen-containing gas and oxygen-containing gas) to the inside and the outside of the hollow MEA, respectively. The electric energy generated by this electrochemical reaction is extracted to the outside via charge collectors arranged on the inside and the outside of the hollow MEA. Namely, the tubular PEFC facilitates extracting the power generation energy by supplying one reaction gas (hydrogen-containing gas and oxygen-containing gas) to the inside of the hollow MEA included in each unit cell and the other reaction gas (oxygen-containing gas or the hydrogen-containing gas) to the outside thereof. Further, the tubular PEFC can use the same reaction gas to be supplied to the outside surfaces of the two adjacent unit cells, so that it is possible to dispense with the separators that also exhibit gas shielding performance in the conventional plane PEFC. Therefore, the tubular PEFC can realize effective downsizing of the unit cells.
Several techniques related to the tubular fuel cells (hereinafter, also simply “tubular FC”) such as the tubular PEFC have been disclosed so far. For example, Japanese National Publication of Translated Version (“Kohyo”) No. 2004-505417 discloses a technique for removing heat generated in a tubular fuel cell (microcell) by extending a length of each of or one of an internal charge collector and an external charge collector (hereinafter, simply “charge collectors”) and contacting a coolant with ends of the charge collectors. The Japanese Kohyo No. 2004-505417 also discloses a technique for forming a modular electrochemical cell assembly by collecting a plurality of microcells and arranging a circularly tubular heat exchange tube between the microcell group. With this technique, it is possible to remove a large amount of heat generated in the microcell group.
However, the former technique disclosed in the Japanese Kohyo No. 2004-505417 is the technique for removing the heat via the charge collectors each configured to include linear members. Because of a long distance between the coolant and a heat generator, heat exchange (cooling) efficiency disadvantageously tends to deteriorate. Moreover, with the latter technique, one circularly tubular heat exchange tube is provided for a plurality of microcells. With the latter technique, heat exchange (cooling) efficiency disadvantageously tends to deteriorate.
It is, therefore, an object of the present invention to provide a fuel cell capable of improving heat exchange efficiency with respect to a tubular fuel cell.